Hierarchical nano-/micro-architecture phonon scattering of p-type Bismuth telluride bulk composites with Ag-TiO2 nano particles synthesized by fluidized bed spray coating method

Abstract

We optimize the thermoelectric (TE) properties by minimizing thermal conductivity utilizing by hierarchical phonon scattering from long to mid wavelength of phonon in p-type Bi0.4Sb1.6Te3.4 (BST) composite with nano Ag-coated TiO2 (Ag/TiO2). We employed an Ag nano particle (20 nm) modulation into TiO2 (500 nm) particles by spray coating method and dispersed in a p-type Bi0.4Sb1.6Te3.4 (BST), giving rise to a hierarchical architecture from nano to micro scale. The nano particle modulation of Ag/TiO2 particles decreases grain sizes of p-type BST matrix. The hierarchical structure of modulating nano particles and small grain sizes of the matrix significantly decreases lattice thermal conductivity due to wide range of wavelength phonon scattering, resulting in the enhancement of thermoelectric performance over a large temperature range. The maximum thermoelectric figure-of-merit zT value reaches to 1.28 for 0.9 wt% Ag/TiO2 modulation doping, which is superior to the other reported ones. The optimized modulating Ag/TiO2 nano-particle dispersion effectively maintains the valence band structure while concurrently mitigating the scattering of charge carriers. Therefore, the nano particle modulation by spray coating method is an effective way to manifest hierarchical architecture from nano to micro-scale phonon scattering, which can be applied in thermoelectric materials design and process.